The continuing goal of this project is to characterize factors that control susceptibility to carcinogen, hormonal and spontaneous mammary carcinogenesis. The focus of this application is to functionally characterize, map and begin to clone a gene which prevents the development of mammary cancer following DMBA, NMU, and/or hormonal treatments. This gene, that is referred to as the mammary carcinoma suppressor (MCS) gene, is a dominant gene acting within the mammary parenchyma. Our aims are to: 1) Map the MCS gene to a specific chromosome region using a co-segregation analysis with minisatellite and microsatellite (SSR) probes. This will be followed by generation of a denser linkage map for the specific chromosome on which MCS resides using a MCS-chromosome specific SSR library; 2) Test the hypothesis that the loss of the MCS gene is required for the induction of mammary carcinomas by chemical carcinogens and ionizing radiation; 3) Test the hypothesis that the MCS gene is involved in mammary gland differentiation, and continue to characterize differential gene expression in mammary epithelial cells associated with the MCS gene; and 4) Initiate efforts to molecularly clone the MCS gene by screening a rat yeast artificial chromosome (YAC) library for clones with MCS-linked markers. Positive clones will be placed in a "contig" map and this contig will then be extended by the isolation of additional overlapping clones. Candidate MCS genes will then be identified using an integrated battery of screening procedures. cDNAs of candidate genes will then be cloned and characterized. Characterization will include an initial assay. Positive sequence will then be tested in vivo for MCS activity screen using a cell culture/in vitro using a transgenic model.